BRBs uncertainty propagation in seismic retrofit of RC structures

Abstract

Passive control systems, such as buckling restrained braces (BRBs), have emerged as an efficient tool for the seismic response control of new and existing structures by providing strength and stiffness to buildings, in addition to high and stable energy dissipation capacity. Systems equipped with BRBs have been widely investigated in literature, however, only deterministic description of the BRBs properties is usually considered. These properties are provided by the manufacturer and are successively validated by qualification control tests. The acceptance criteria specified by codal standards allows for some variation in the response of a single BRB by introducing a tolerance limit. Therefore, the real properties of these devices could differ from the design values. This difference can affect the seismic response and potentially lead to an undesired seismic performance at the global level. This paper provides some preliminary insights on the influence of the BRBs uncertainty on the seismic response of a retrofitted RC frame. For the case-study, a benchmark two-dimensional RC frame is considered. A single retrofit condition is analyzed and the BRBs uncertainty is defined according to the tolerance limits of devices quality control tests. Cloud analysis and probabilistic seismic demand models are used to develop fragility functions for four different damage states. Fragility curves are defined for the bare and retrofitted frame while considering both the design and the real values of the BRBs properties. The preliminary results show that the BRBs uncertainty could lead to an increase of the vulnerability up to 26.80% for the considered case-study.